Clinical Science (38)

Abstract

Effect of peripheral morphine in a human model of acute inflammatory pain. (Hvidovre University Hospital, Hvidovre, Denmark) BR J Anaesth 2000;85:228–232.This study used a randomized, double‐blinded, placebo‐controlled, three‐way crossover design in a human model of acute inflammatory pain (heat injury). Eighteen healthy volunteers were studied who each received morphine locally (2 mg), morphine systemically (2 mg), or placebo on three separate study days. The subjects received morphine infiltration subcutaneously (s.c.) 1 h before heat injury (47°C, 7 min) and naloxone infiltration s.c. (0.2 mg) 2.5 h after the heat injury. Hyperalgesia to mechanical and heat stimuli were examined using von Frey hairs and thermodes, and pain was rated using a visual analogue scale. The burns produced significant hyperalgesia, but local morphine infiltration neither reduced pain during the burn, nor primary or secondary hyperalgesia to mechanical and heat stimuli after the burn. Conclude peripherally applied morphine had no acute antinociceptive effects in this human model of acute inflammatory pain. Comment by Hemmo A. Bosscher, MD.This study is well controlled for placebo effect and the systemic effect of subcutanuously injected morphine. One of the few criticisms that can be made is the amount of narcotic injected. This may not be enough to bind to a sufficient number of receptors. One would expect some role for peripheral opioid receptors. The other comment would be that this type of injury (mainly small fiber involvement in this case) does not represent all types of nociception and, therefore, the peripheral action of morphine can not be excluded for different types of nociception. But overall this is a convincing study, consistent with the literature.